As described in U.S. Pat. No. 6,108,555; “Enhanced Time-Difference Localization System” and U.S. Pat. No. 6,119,013; “Enhanced Time-Difference Localization System” both by Maloney et al and owned by TruePosition Inc. and included herein via reference, use of collateral information as a factor in the calculation of a location estimate for a voice or data wireless caller can increase the accuracy of a wireless location system both for the current call and overall. Use of historical calling patterns with associated location information offers a new avenue for improving location accuracy for all location technology types.
Digital wireless cellular networks provide coverage to a geographic area by locating cell sites throughout that area. The range of a cell site's coverage is determined by the height of the transmit/receive antenna(s), the transmitter's power output, the spatial response of the antenna(s) and their orientation. Omnidirectional sites utilize antennas that transmit RF energy equally in all directions from the cell site. Sectored sites utilize antennas that transmit energy in a smaller portion of the 360 degree angular range.
Typically, sectored sites will divide the 360 degree angular range into three equiangular regions. Three antennas will be utilized with azimuthal beamwidths of 120 degrees and pointed at three uniformly spaced azimuth angles, i.e. 0 degrees, 120 degrees and 240 degrees. Sectored cell sites are utilized to increase the capacity, i.e. the number of wireless calls it can handle simultaneously, by approximately a factor of three. This sectored approach will still provide omnidirectional coverage but increased capacity over the this service area.
Wireless digital communications systems require the handset and cell site to be synchronized in time to certain accuracy. As an example, the well-known Global System for Mobility (GSM) is a time-division-multiple-access (TDMA), frequency-division-multiple-access (FDMA) digital communications system using frequency separated carriers, each carrier with eight time slots per TDM frame permitting up to eight simultaneous phone calls on a single frequency. Thus, for maximum capacity, each mobile station (MS) is assigned a time slot and must only transmit in that time slot. Each time slot is 577 microseconds in duration. GSM handsets can adjust their time of transmission in increments of 1.8 microseconds. Since radio waves propagate at a constant velocity this also corresponds to a range width, or band, of 554 meters. Thus, a GSM base station will instruct a handset to adjust their time of transmission so that it is transmitting in the correct time slot. This process of time synchronizing the handset to the base station also permits the base station to determine the range the handset is from it. In GSM networks this range value is derived from the timing advance (TA) value that the GSM network determines for each mobile so that it transmits at the correct time and duration for efficient wireless communications. In sectored cell sites this range value and sector information, i.e. in GSM the Cell Global Identity (CGI), can be used to approximate the location of mobile. This type of location estimate is commonly known as Cell Global Identity plus Timing Advance (CGI+TA). The CGI thus corresponds to a cell when omni-directional antenna is used and a sector of a cell when directional (i.e. sectored) antennas are used.
In the evolved Universal Mobile Telephony System Terrestrial Radio Access Network (eUTRAN), also known as the Long-Term-Evolution (LTE) system, as another example; the Orthogonal Frequency Division Modulation (OFDM) radio access network uses scalable radio resources for each session (voice or data). The LTE bandwidth is a divided into sets of 15 kHz subcarriers. These subcarriers grouped by 12's into 180 kHz bands. Each band is divided in time into 0.5 millisecond slots and the slots are grouped into 1.0 millisecond subframe. The 12 subcarriers bandwidth and single subframe (two 0.5 ms timeslots) are each 1 resource block (RB). With a subcarrier bandwidth of 15 KHz, the LTE symbol period is set to 66.7 microseconds. The symbol length is equal to the reciprocal of the carrier spacing so that orthogonality as required by the OFM modulation scheme is achieved.
The LTE Timing Advance (Tadv) as defined in Third Generation Partnership (3GPP) Technical Specification section 7.3, “Timing Advance”. The Tadv is specified in units of (16*Ts), and the mobile must adhere to it with an accuracy of (4*Ts).Ts=1/(15,000*2048)˜=32.55×10−9 seconds.
So, Tadv has a resolution of 520.8333 nanoseconds, and is adhered to with an accuracy of ˜130.2 nanoseconds by the UE. Since radio waves propagate at a constant velocity this also corresponds to a range width, or band, of 156 meters for LTE. In LTE, the cell and sector identification (which corresponds to a geographic location) is encoded in the Physical Cell ID (PCI) rather then a unique CGI (as in GSM) for each sector of the service area.
Similar timing bands can be computed for other wireless communications systems using either timing settings or chip rates. Use of mobile transmit power can also be used as a range estimate if the transmit power is known, allowing computation of path-loss.
Wireless location technologies can be grouped as network-based or mobile-based characterized by the point of signal reception.
Network-based location solutions use specialized receivers and/or passive monitors within, or overlaid on, the wireless communications network to collect uplink (mobile device-to-base station) signaling used to determine location and velocity of the mobile device. Network-based location estimation techniques include uplink Time-Difference-of-Arrival (TDOA), Angle-Of-Arrival (AOA), Multipath Analysis (RF fingerprinting), and signal strength measurement (SSM).
Mobile-device based location solutions use specialized electronics and/or software within the mobile device to collect signaling. Location determination can take place in the device or information can be transmitted to a landside server which determines the location. Mobile Device-based location estimation techniques include CID (serving Cell-ID, e.g. the CGI for GSM and the PCI for LTE), CID+TA (serving cell-ID plus time-based ranging), Enhanced Cell-ID (ECID, a serving cell, time-based ranging and power difference of arrival hybrid), Advanced-Forward-Link-Trilateration (AFLT), Enhanced Observed Time Difference (E-OTD), Observed-Time-Difference-of-Arrival (OTDOA) and Global Navigation Satellite System (GNSS) positioning. A current example of a GNSS system is the United States NavStar Global Positioning System.
Overviews of example standardized location techniques can be found in Third Generation Partnership Program (3GPP) Technical Specification 23.271, “Functional stage 2 description of LoCation Services (LCS)” (Release 10), in the Third Generation Partnership Program 2 (3GPP2) specifications C.S0022-0 and C.S0022-A, the Institute of Electrical and Electronic Engineers (IEEE) standard 802.16e-2009 Annex K, and the Open Mobile Alliance (OMA) Secure User Plane Location (SUPL V2.0) specification.
Hybrids of the network-based and mobile device-based techniques can be used to generate improved quality of services including speed, accuracy, yield, and uniformity of location. A geographic position estimate, an altitude estimate, a speed estimate and a heading can all be derived using one or more wireless location technologies as hybrids.
Since the advent of cellular telecommunications in the 1980's, and especially in the past two decades, the cellular industry has increased the number of air interface protocols available for use by wireless telephones, increased the number of frequency bands in which wireless or mobile telephones may operate, and expanded the number of terms that refer or relate to mobile telephones to include “personal communications services,” “wireless,” and others. The air interface protocols now used in the wireless industry include AMPS, N-AMPS, TDMA, CDMA, GSM, TACS, ESMR, GPRS, EDGE, UMTS/WCDMA, WiMAN, WiMAX, LTE (eUTRAN), LTE Advanced and others.